Traditionally, removal of ice from airplanes is done in two main steps, the first step being a de-icing step, wherein ice and snow deposited on the surface of the airplane is removed, the second step being an anti-icing step, wherein the surface of the airplane is covered with a protective liquid, which precludes formation of new ice on the surface of the airplane.
In the de-icing step it is known to use a pre-heated liquid, which is a mixture of water and a so called Type 1 de-icing liquid. The Type 1 de-icing liquid has a low viscosity and it is primarily the thermal energy of the liquid, which causes the melting and removal of the ice (and possible snow deposits) from the airplane.
Typically, a Type 1 liquid is a pre-mixed liquid having propylene or ethylene glycol as the main constituents. In addition to this a typical Type 1 liquid comprises a number of so called additives. These additives can for example be agents, which raise the flash point, or which reduce the tendency of formation of foam, or which are anti corrosive, or a mixture of all these, or other, agents.
The Type 1 liquid can be applied to a surface of an airplane in undiluted form, in which form it has the lowest freezing point, or it can be delivered in a premix of for example 50% or 75% Type 1 fluid mixed with water. It is customary to use these mixtures, at higher temperatures, where a higher freezing point of the de-icing liquid can be allowed. A typical Type 1 liquid is constituted by 88% propylene or ethylene glycol, 10% water and 2% additives.
The anti-icing step is performed by applying a protective layer of anti-icing liquid on the surface of an airplane in order to prevent the formation of a new layer of ice on the surface of the airplane before it has left the runway.
The liquid, which is used for anti-icing is a liquid with a rather high viscosity (around 20.000 cST to around 30 000 cSt). The high viscosity of the anti-icing liquid is achieved by adding polymers, which form long molecular strings in the anti-icing liquid. These molecular strings are rather sensitive to mechanical influence from the nozzle through which the anti-icing fluid is sprayed onto the outer surface of the airplane. This is due to the fact that these molecular strings can be broken into smaller pieces in the nozzle. Therefore, the anti-icing liquid is sprayed onto the outer surface of an airplane with a rather low and controlled pressure gradient (pressure drop) through the nozzle, whereby it is avoided that the mechanical influence will become too big. It is furthermore desirable to apply a uniform rather thin layer of the anti-icing liquid to the outer surface of the airplane. Hence, the anti-icing liquid is also sprayed onto said surface at a rather low flow rate, e.g. around 100 l/min.
The anti-icing liquid is called a Type 2 or Type 4 liquid, where the Type 4 liquid has a higher viscosity than the Type 2 liquid. A typical Type 2 or Type 4 liquid consists of 50% propylene or ethylene glycol, 48% water and 2% polymers and additives.
De-icing and anti-icing liquids are traditionally supplied to the airports or service companies, which perform de- and anti-icing for the airports, as Type 1, Type 2 or Type 4 liquids, which airports or service companies need to build up large stocks of these liquids before onset of winter. Moreover, since these liquids are produced by relatively few producers in the world it is often necessary to build up a rather large stock of these liquids in order to secure enough supplies to last a whole winter season. Furthermore, the scarcity of producers of these liquids also means that acquisition of these liquids incur rather big transport expenses in addition to the environmental problems related to the transportation of these liquids around the world. A wrong estimate of how long or hard a winter season will be may thus lead to a situation, wherein the airports and/or before mentioned service providers may run out of de- and anti-icing liquids.